Transfer Coefficients in a Packed Column

SAHAY, B. N. and SHARMA, M. M. Chem.Eng. Sci. 28 (1973) 41. Effective interfacial areas and liquid and gas side mass transfer coefficients in a packed column. 

Example 12 Mass-Transfer Coefficients in a Packed Column... 

Ponter, A. B. and Au-Yeung, P. H., Estimating Liquid Film Mass Transfer Coefficients in Randomly Packed Columns, in Handbook of Heat and Mass Transfer, Cheremisinoff, N. P. (Ed.), Gulf Publishing Corp., Houston, TX, Chap. 20, Vol. II, pp. 903-952, 1986. 

Example 2.3 Mass-Transfer Coefficient in a Packed-Bed Distillation Column... 

The method is developed in two variants differing in the kind of the laboratory column used. In die first one, this is a column with a single sphere [35, 36], and in the second - with a vertical column of spheres [37]. In both oases the mass transfer process is liquid-side controlled absorption. The method accepts that the mass transfer coefficients in a packing and on spheres are the same, and that the effective surfiice of the spheres is equal of dieir geometrical surfiice. Because the mass transfer coefficient depends on the hjrirodynamics of the liquid phase, and die hydrodynamics - on of die form of the packing, the first acceptation is doubtfiil. 

The variation of efficiencies is due to interaction phenomena caused by the simultaneous diffusional transport of several components. From a fundamental point of view one should therefore take these interaction phenomena explicitly into account in the description of the elementary processes (i.e. mass and heat transfer with chemical reaction). In literature this approach has been used within the non-equilibrium stage model (Sivasubramanian and Boston, 1990). Sawistowski (1983) and Sawistowski and Pilavakis (1979) have developed a model describing reactive distillation in a packed column. Their model incorporates a simple representation of the prevailing mass and heat transfer processes supplemented with a rate equation for chemical reaction, allowing chemical enhancement of mass transfer. They assumed elementary reaction kinetics, equal binary diffusion coefficients and equal molar latent heat of evaporation for each component. 

The only reported-study on heat transfer is by Weekman and Myers.105 They measured wall-to-bed heat-transfer coefficients in a cocurrent air-water downward flow through a packed column. Three types of packings. 0.65-cm alumina spheres, 0.475-cm glass spheres and 0.38-cm TCC beads were examined. The heat-transfer coefficients were much higher than those observed for single-phase liquid flow. The transition from homogeneous to pulsed flow corresponded to an increase of... 

Most recently. Kirillov and Nasamanyan15 carried out a very interesting unsteady-state analysis of liquid-solid mass transfer for cocurrent upflow in a fixed-bed reactor. The analysis was compared and verified by the steady-state measurements of liquid-solid mass-transfer coefficients in a 10-cm x 10-cm square column with a height of 50 cm. Three types of packings, 30-mm and 8-mm... 

Yin et al. (2000) developed a computational model to simulate flow and mass transfer in randomly packed distillation columns. It is necessary to develop appropriate models for interphase drag and dispersion coefficients. The general approach is to represent the overall pressure drop for gas-liquid flows in a packed column in two parts, namely wet and dry ... 

Doan, H.D. Fayed, M.E. Entrance effect and gas-film mass-transfer coefficient in a large-diameter packed column. Ind. Eng. Chem. Res. 2000, 39 (4), 1039-1047. 

Estimate the mass transfer coefficients, interfacial area, and the heights of transfer units for the system acetone (l)-water (2) in a packed column under the following conditions prevailing near the top of the column ... 

The nonequilibrium stage in Figure 14.1 may represent either a single tray or a section of packing in a packed column. In the models described in this chapter the same equations are used to model both types of equipment and the only difference between these two simulation problems is that different expressions must be used for estimating the binary mass transfer coefficients and interfacial areas. 

Although reliable correlations of mass transfer coefficients for the components of a multicomponent mixture remain to be developed, a development of the equations required to describe simultaneous mass and heat transfer in a packed column follows. 

A wastewater stream of 0.038 m3/s, containing 10 ppm (by weight) of benzene, is to be stripped with air in a packed column operating at 298 K and 2 atm to reduce the benzene concentration to 0.005 ppm. The packing specified is 50-mm plastic Pall rings. The airflow rate to be used is five times the minimum. Henry s law constant for benzene in water at this temperature is 0.6 kPa-m3/mol (Davis and Cornwell, 1998). Calculate the tower diameter if the gas-pressure drop is not to exceed 500 Pa/m of packed height. Estimate the corresponding mass-transfer coefficients. The diffusivity of benzene vapor in air at 298 K and 1 atm is 0.096 cm2/s the diffusivity of liquid benzene in water at infinite dilution at 298 K is 1.02 x 10 5 cm2/s (Cussler, 1997). 

Norman, W.S., and Sammak, F.YY (1963), Gas absorption in a packed column part I The effect of liquid viscosity on the mass transfer coefficient, Transactions of the Institution of Chemical Engineers, 41(3) 109-116. 

A comprehensive study of the stripping of carbon dioxide from monoethartolamine solutions in a packed column is described by Weiland et at. " These investigators develed a design approach that uses only fundamental physicochemical data and tested the approach against 173 experiments on the mass transfer performance of a pilot scale stripping column. Predicted mass transfer coefficients agreed with observed values within 25%. 

In the presentation the nonequilibrium model for the calculation of the three-phase distillation in a packed column is presented. The model considers the mass transfer between all three existing phases. A remarkable point is that by using normal two-phase methods mass transfer coefficients and interfacial areas can be calculate in a first step. The study is strongly influenced by the interaction between the development of the model and the experiments. The validation was carried out in a packed column of the institute on experiments at total and finite reflux. Two different heterogeneous azeotropic mixtures have been separated by distillation. The distillation run at finite reflux showed an unusual behaviour, which is based in the heterogeneity of the liquid phase. In this case a nonequilibrium model is needed. A comparison of the simulation results and the experimental specifications shows the performance of the developed... 

To determinate the mass transfer coefficients in a given model the experimental results have to be calculated using the same model. The method [74, 77] proper for packed bed columns for dispersion model is based on flie analytical solution of Sleicher [78], and Miyauchi and Vermeulen [79]. This solution gives the possibility to calculate the concentration profile in the packing, knowing the Bodenstein numbers and the mass transfer coefficient. Using an iteration procedure, it is possible, at given initial and end concentrations, to obtain also the respective mass transfer coefficient. The... 

In 1966, in a paper that now is considered a classic, Danckwerts and Gillham [Tmns. Inst. Chem. Eng., 44, T42 (1966)] showed that data taken in a small stirred-ceU laboratoiy apparatus could be used in the design of a packed-tower absorber when chemical reactions are involved. They showed that if the packed-tower mass-transfer coefficient in the absence of reaction (/cf) can be reproduced in the laboratory unit, then the rate of absorption in the l oratoiy apparatus will respond to chemical reactions in the same way as in the packed column even though the means of agitating the hquid in the two systems might be quite different. 

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